Combeite Mineral Data

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General Combeite Information

Chemical Formula:

Na2Ca2Si3O9

Composition:

Molecular Weight = 354.39 gm

Sodium 12.97 % Na 17.49 % Na₂O

Calcium 22.62 % Ca 31.65 % CaO

Silicon 23.78 % Si 50.86 % SiO₂

Oxygen 40.63 % O

______ ______

100.00 % 100.00 % = TOTAL OXIDE

Empirical Formula:

Na₂Ca₂Si₃O₉

Environment:

In nephelinite (Mt. Shaheru, Congo); in nephelinite and ash ejecta (Oldoinyo Lengai volcano, Tanzania).

IMA Status:

Valid Species (Pre-IMA) 1957

Locality:

On Mt. Shaheru, the extinct southern cone of Mt. Nyiragongo, Kivu Province, Congo (Zaire). Link to MinDat.org Location Data.

Name Origin:

Named for Arthur Delmar Combe, Geological Survey of Uganda.

Combeite Image

Images:

Combeite

Comments: Crystalline cleavage fragment of combeite.
Location: Mont Saint Hilaire, Quebec, Canada. Scale: See Photo.
© Jeff Weissman / Photographic Guide to Mineral Species

Combeite Crystallography

Axial Ratios:

a:c = 1:1.25839

Cell Dimensions:

a = 10.48, c = 13.188, Z = 6; V = 1,254.39 Den(Calc)= 2.81

Crystal System:

Trigonal - TrapezohedralH-M Symbol (3 2) Space Group: P 3₂21,P 3₁21

$Help on X Ray Diffraction:$ X Ray Diffraction:

By Intensity(I/I_o): 2.657(1), 2.607(0.8), 3.304(0.7),

Crystal Structure:

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Ohsato H , Maki I , Takeuchi Y , Acta Crystallographica, Section C , 41 (1985) p.1575-1577, Structure of Na2CaSi2O6, Locality: synthetic high-temperature form

View Additional jPOWD Structure files for Combeite
[1] [2] [3]

Physical Properties of Combeite

Cleavage:

None

Color:

Colorless.

Density:

2.844

Diaphaneity:

Transparent

Streak:

white

Optical Properties of Combeite

Gladstone-Dale:

CI meas= -0.023 (Excellent) - where the CI = (1-KPDmeas/KC)
CI calc= -0.036 (Excellent) - where the CI = (1-KPDcalc/KC)
KPDcalc= 0.2128,KPDmeas= 0.2103,KC= 0.2055
Ncalc = 1.58

Optical Data:

Uniaxial (+), w=1.598, e=1.598, bire=0.0000.

Calculated Properties of Combeite

Electron Density:

Bulk Density (Electron Density)=2.82 gm/cc
note: Specific Gravity of Combeite =2.84 gm/cc.

Fermion Index:

Fermion Index = 0.01
Boson Index = 0.99

Photoelectric:

PE_Combeite= 3.90 barns/electron
U=PE_Combeite x rElectron Density= 11.01 barns/cc.

Radioactivity:

GRapi = 0 (Gamma Ray American Petroleum Institute Units)
Combeite is Not Radioactive

Combeite Classification

Dana Class:

61.01.02a.05 (61)Cyclosilicate Six-Membered Rings

(61.01)with [Si6O18] rings; possible (OH) and Al substitution

(61.01.02a)Lovozerite group (HEX and HEX-R subgroup)

61.01.02a.01 Lovozerite H4Na2Ca(Zr,Ti)[Si6O18] R 3m 3 2/m

61.01.02a.02 Kazakovite Na6MnTiSi6O18 R 3m 3 2/m

61.01.02a.03 Tisinalite Na3H3(Mn,Ca,Fe)TiSi6(O,OH)18•2(H2O) R 3m 3 2/m

61.01.02a.04 Zirsinalite Na6(Ca,Mn,Fe)Zr[Si6O18] R 3m 3 2/m

61.01.02a.05 Combeite Na2Ca2Si3O9 P 3₂21,P 3₁21 3 2

61.01.02a.06 Kapustinite! Na5.5Mn0.25ZrSi6O16(OH)2 C 2/m 2/m

Strunz Class:

09.CJ.15 09 - SILICATES (Germanates)

09.C - Cyclosilicates

09.CJ -[Si6O18]12- 6-membered single rings (sechser-Einfachringe),

09.CJ.15 Combeite Na2Ca2Si3O9 P 3₂21,P 3₁21 3 2

09.CJ.15 Kazakovite Na6MnTiSi6O18 R 3m 3 2/m

09.CJ.15 Lovozerite H4Na2Ca(Zr,Ti)[Si6O18] R 3m 3 2/m

09.CJ.15 Zirsinalite Na6(Ca,Mn,Fe)Zr[Si6O18] R 3m 3 2/m

09.CJ.15 Kapustinite! Na5.5Mn0.25ZrSi6O16(OH)2 C 2/m 2/m

09.CJ.15 Tisinalite Na3H3(Mn,Ca,Fe)TiSi6(O,OH)18•2(H2O) R 3m 3 2/m

09.CJ.15 Litvinskite! Na2([],Na,Mn)Zr[Si6O12(OH,O)6] Cm m

Other Combeite Information

References:

NAME( AntBidBlaNic2) PHYS. PROP.(Enc. of Minerals,2nd ed.,1990) OPTIC PROP.(Enc. of Minerals,2nd ed.,1990)

See Also:

Links to other databases for Combeite :
1 - Am. Min. Crystal Structure Database
2 - Athena
3 - EUROmin Project
4 - Ecole des Mines de Paris
5 - GeoScienceWorld
6 - Google Images
7 - Google Scholar
8 - Handbook of Mineralogy (MinSocAm)
9 - Handbook of Mineralogy (UofA)
10 - MinDAT
11 - Mineralienatlas (Deutsch)
12 - Online Mineral Museum
13 - QUT Mineral Atlas
14 - Ruff.Info
15 - WWW-MINCRYST

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Print or Cut-and-Paste your Combeite Specimen Label here :

Combeite

Na2Ca2Si3O9
Dana No: 61.01.02a.05 Strunz No: 09.CJ.15
Locality:

Notes: